Sputtering of gold foils in a high voltage electron microscope A comparison of theory and experiment

Abstract

Evaporated (111) gold foils 200–1000 A thick have been irradiated with electrons in a high voltage electron microscope at energies from 0·5 to 1·1 MeV to study the sputtering behaviour. Transmission-sputtered atoms were collected on a carbon film and their spatial distribution was determined by X-ray microanalysis. The angular distribution of sputtered intensity was found to be strongly energy-dependent, exhibiting a single central maximum for 0·5 MeV and three symmetrically disposed maxima for energies above 0·6 MeV, all of which became increasingly sharp at higher energies.

The main features of the results are explained at an atomic level with the aid of a molecular dynamics programme, and the roles of collision sequences, steering of trajectories by neighbouring atoms, and thermal vibration effects are elucidated. We find that, at energies <0·6 MeV, surface atoms are sputtered by direct recoils only, whereas, at energies > 0·6 MeV, up to ∼40% of the total yield comprises surface atoms sputtered by sub-surface recoils which generate focused collision sequences down 〈110〉 directions.